1. Field of the Invention
The present invention relates to communications systems in general and, more particularly, to local area networks (LANs) which transmit high frequency and low frequency signals.
2. Prior Art
Because of the different types of machines which are now available for use in the home and in the office, the need arises for a common communications system which is able to transmit mixed information. The prior art has recognized the need for such a system and has provided the so-called Data Over Voice (DOV) communications system.
The DOV communications system is a known technique for simultaneously transmitting and receiving an analog voice signal and a digital data signal through a common 2-wire signal line. This is a band division system in which the digital data is FSK modulated on a high frequency carrier signal and is superimposed on a signal line. Thus, it is easy to separate the high frequency FSK modulated data signal from the low frequency voice signal by a filter circuit. A more detailed description of the DOV system is set forth in U.S. Pat. No. 4,670,874. Included in the drawbacks of this system is the fact that it provides limited bandwidth usage. Thus, certain frequencies within the transmission spectrum are not available for use.
Other art teaching the transmission of two signals over the same line is set forth in U.S. Pat. No. 1,812,624. Other techniques describing the use of transformers for suppressing noise in a transmission line are set forth in U.S. Pat. No. 3,223,920.